The overall goal is to examine the contribution of low levels of energy expenditure to the development of obesity in Native American, Mohawk children. Prospective studies will be performed using two models of human obesity: 1) young children (4 to 6 years) of obese Mohawk parentage, and 2) young children (4 to 6 years) of obese, non-Mohawk, Caucasian parentage, using children of lean parentage as controls in both groups. The specific objectives are to: 1) Characterize energy expenditure, physical activity, body composition and fat distribution in field studies in Mohawk children of lean and obese parents, as compared to young children in Chittenden County, Vermont of lean and obese parents; 2) Examine the association between low levels of energy expenditure and physical activity to prospective body fat and weight gain over 12 months in young Mohawk children, as compared to young children in Chittenden County, Vermont; 3) Establish an obesity data base in Mohawk children to provide a set of baseline values which can be used in the evaluation of the effectiveness of future intervention programs. Total energy expenditure will be measured over 14 days under free-living conditions with doubly labeled water, resting energy expenditure by indirect calorimetry and physical activity by the difference between total and resting energy expenditure. Body composition will be measured by a variety of techniques including total body water, densitometry, body impedance analysis and skinfolds. The study will test the following hypothesis: 1) Children with low total energy expenditure are more susceptible to the development of obesity over time because they are less likely to match energy intake to energy expenditure. Furthermore, low rates of total energy expenditure will be explained by low physical activity, rather than reduced resting energy expenditure. 2) The contribution of inactivity and low total energy expenditure to the development of obesity will not be specific to Native American children, thus disproving a genetic predisposition to the development of obesity in the Mohawk population. These pilot studies will form the basis of further studies to examine the potential role of lifestyle interventions (eg. dietary manipulation, exercise prescription) that can manipulate energy expenditure and/or substrate utilization in a manner that will prevent the development of obesity.